Throat plate



United States Patent 3,423,963 THROAT PLATE Gus T. Smith, Paducah, Ky., assiguor to Ace Engineering Co., Paducah, Ky., a corporation of Kentucky Continuation of application Ser. No. 465,019, June 18, 1965. This application Oct. 30, 1967, Ser. No. 679,266 US. Cl. 66125 3 Claims Int. Cl. D04b 15/38 ABSTRACT OF THE DISCLOSURE This application is a continuation of application Ser. No. 465,019, filed June 18, 1965, now abandoned. This invention relates to wear-resistant throat plate for knitting machines and the like and is concerned more particularly with an improved mode of connection between a yarnengaging section of hard, abrasion-resistant ceramic material and a base or supporting section of metal or the like.

The problem of extreme wear of various yarn guides employed in the textile field caused by the erosive effect of the strand passing therethrough, especially in the case of the newer synthetic fibers and filaments, is too wellknown to require detailed recapitulation, as in the existence of a veritable plethora of suggestions aimed at solving this problem. Many of these suggestions basically involve the provision of wear-resistant ceramic material at each site of concentrated wear in order to utilize the acknowledged superiority in abrasion-resistance of this material over available steels, even when specially hardened. For most types of guides, the addition of a ceramic reinforcement at a given point of wear is not overly difficult to accomplish, it being merely necessary to mount a ceramic element at an appropriate point on the guide. In the case of a throat plate for a knitting machine, however, several peculiar requirements combine to considerably complicate the addition of a ceramic section.

Thus, the throat plates for most circular knitting machines are supported roughly in cantilevered fashion with the yarn-engaging edge at a free extremity where support for a ceramic section is awkward to furnish. Moreover, the central section of the plate is subject to repeated impact as the yarn feed fingers move into and out of feeding position and such impact cannot be tolerated by the brittle ceramic if this material were to form this section or the plate as a whole. Again, wear is ordinarily concentrated at a complex junction of a plurality of horizontal and vertical surfaces, precluding a simple overlay of ceramic upon the surface of the Wear point. Finally, the location of the plate directly above the needle array imposes a severe penalty for inadequate design since if any part of the plate were to become detached, it drops into the needle array, causing costly smash-ups.

From the aforegoing, it will be understood that the provision of a ceramic member at the required point on a throat plate presents a formidable problem of mechanical attachment, which the various proposals heretofore made have solved with varying degrees of success. Among the more successful have been those disclosed in U.S.P.

3,004,733 and 3,095,718, commonly assigned with this application, which are based essentially upon an interlocking configuration between the ceramic yarn-engaging section and a base section of steel or the like. While the constructions illustrated in these patents have Worked well in practice, they are rather expensive and time-consuming to assemble, because of the complicated shape and close-tolerances essential to the interlock.

It has now been discovered that a yarn-engaging ceramic section of relatively plain, inexpensive conformation can be cheaply and effectively attached to a metallic base section through the medium of a soldered joint, where the surface of the ceramic section at the joint bears a metallized coating of a metal capable of being wetted by the solder or a plating of such a metal.

One illustrative embodiment of a throat plate constructed in accordance with this invention is shown in the accompanying drawings in which:

F IG. 1 is a top plan view;

FIG. 2 is a right side elevation;

FIG. 3 is a simplified perspective view of the plate in operative association with a typical yarn feed finger and a few of the knitting needles of the knitting machine, the latter being indicated diagrammatically and all other parts of the machine being omitted for sake of clarity and simplification; and

FIG. 4 is an enlarged cross-sectional view showing the soldered joint between the metallic base section and ceramic section in detail.

Turning now to a more detailed description of the present invention, the type of throat plate to which the present concept can be applied is a matter of almost complete indifference and throat plates in virtually any of the conformations known in the art are subject to modification to embody the concept of the present invention. In order to provide a specific basis for this description, however, one typical throat plate has been selected to serve as an illustrative example, as can be seen from the accompanying drawings This particular plate has the general conformation of a fairly flat, generally rectangular block that is usually produced by machining good quality steel, such as tool steel or the like. In the present invention, the throat plate is a composite of a front yarn-engaging portion 10 formed of wear-resistant ceramic material, to be described more in detail subsequently, and a base or supporting portion 12 which is formed of the just-mentioned steel block, these two sections together defining what normally in the art has been a single integral member. With the exception of the front face 14 of the ceramic section 1.0 and the top face of the composite member, the shape of the remaining sides of the member is of no importance and is determined by the spatial considerations at the operative site on the knitting machine, although the usual practice in the art is for these sides to have a normal perpendicular relationship as depicted in the drawings.

A longitudinal channel 16 extends in the top face in the composite member from one end to the other. During operation, as indicated in FIG. 3, the yarn feed fingers are received Within this channel in the region of the base section 12 with the yarn stretching therefrom through the ceramic portion of channel 16 to the knitting needles N. In the full thickness regions of the supporting section 12 flanking channel 16, are providedapertures 18, 18 for use in attaching the composite plate into operative position on the undcrsurface of the latch ring of the knitting machine. Preferably, these holes 18, 18' are elongated in a direction parallel to channel 16 in order to facilitate precise adjustment of the front face of the plate radially with respect to the cylinder of the knitting machine. Easier access to the apertures 18, 18 for introduction of the mounting screws can be had if the undersurface of the supporting section 12 in the region of the apertures is recessed as at 20, 20'. Dependent upon the type of circular knitting machine in which the plate is to be employed, a transversely elongated aperture 22, best seen in FIG. 1, may be provided in the floor of channel 16, in the vicinity of the junction between the two sections 12 and 14, that is, about one-third of the total length of the channel 16 from the inner or front edge of ceramic section 10. For other types of knitting machines, the floor of the channel may be left intact.

The front face of ceramic section is given the configuration that normally appears in the throat plates of the prior art. Thus, the face 14 has a shallow generally convex curvature, the radius of which is selected so as to conform to the curvature of the cylinder of the knitting machine. Preferably, the inside upper corners of face 14 defined by channel 16 are beveled very slightly as indicated at 24.

The mutually adjacent surfaces of the section 10 and 12, respectively, must be so shaped as to fit generally smoothly together or, in other words, be of substantially mating configuration. For sake of simplicity of construction, it is preferred that these surfaces extend in transverse planar relationship relative to this axis of channel 16 but this particular relationship is not critical to the successful practice of the invention. They could, for example, be of complementary inclination when viewed in side elevation or in the shape of a shallow triangle or trapezoid, for instance, when viewed in plan, to mention just a few of the possibilities that will occur to one skilled in the art.

In accordance with the present invention, the complementary face 26 of the ceramic section 10 of the throat plate bears a metallized coating, indicated at 30, extending substantially over the entire facial area thereof and the surface thus coated is attached to the complementary face 28 of the supporting section 12 by soldering to give a solder joint indicated at 32. It is now possible to obtain on the commercial market ceramic material of the type meeting the requirements of the present invention that has been already metallized along any selected area, or to have the metallization carried out on ceramic parts obtained from commercial sources. The ceramic material suited to the present invention is now so well-known in the art that a detailed description thereof is hardly necessary, particularly since additional information can be obtained from the aforementioned patents as well as other sources available in the art. A preferred ceramic is that sold under the trade name AlSiMag. This trade name is applied by the manufacturer to a broad range of considerably varying materials, not all of which are equally advantageous here. Within the broad class carrying this designation, the so-called alumina ceramics sold under the trade names AlSiMag 576, 614, 719 and 748 are particularly desirable. These materials have a content of alumina ranging from about 85 to 98% or more, by weight a hardness on the Mohns scale of 9 and on the Rockwell 45N scale of 72-78, a flexural strength of 35,000 to 52,000 and an impact resistance of 6.3-7.5. In addition to the valuable combination of mechanical properties just recited, the alumina ceramics have been found to be well adapted for application of a metallized coating thereto.

For a general description of the several techniques that have been developed for metallizing ceramics, reference can be had to Bulletin No. 632 published by the American Lava Corporation of Chattanooga, Tenn. Briefly, these techniques fall into two categories, those carried out at high temperatures, and those carried out at low temperatures. One high temperature method makes use of an active metal, such as titanium, which, under conditions of high temperature and vacuum, will combine with one of the transition metals, such as silver or nickel, to form a molten solution and in this condition react with the ceramic oxide to form a strong chemical bond. In another,

refractory metal powder, usually powdered molybdenum or its oxide, alone or in combination with catalytic material sudh as manganese, iron, nickel, titanium, chromium, silica, calcium, or glass frit, is suspended in a temporary liquid binder and applied to the designated area of the ceramic, after which the coating is dried and sintered in a protective atmosphere. To facilitate soldering of the sintered coating, it may be electroplated as with nickel and then sintered in a protective atmosphere at a lower temperature for better adherence and reduced susceptibility to oxidation.

While the high temperature procedures just summarized can be employed here, they are somewhat more complicated and expensive than is actually necessary. Consequently, the preferred practice is to use a low temperature metallizing step in which, in general, a silver-containing coating composition, such as a paste of silver in an oily carrier or a paste of silver and glass frit, is applied to the designated area of the ceramic, dried and then fired in a kiln to produce a good bond between the silver coating or lining and the surface of the ceramic. The silver lining thus produced tends to oxidize if left exposed to the atmosphere for considerable time so as to cause difficulties during soldering. To avoid this, the silver lining can be electroplated with any suitable less-oxidizable metal such as copper, nickel or tin, to which the selected solder will wet and adhere. Aternatively, the oxidation can be allowed to proceed and the surface to be soldered cleaned just prior to soldering by chemical means such as the application of nitric acid or mechanical means such as sandblasting or buffing with a wire brush.

As is well-known in the art, circular knitting machines are subject to vibration during operation and it is important to the practice of the present invention that the solder selected for joining the metallized ceramic and base sections together be of a type that is not likely to rupture as a result of vibration. Soft solders, such as those composed of tin and lead, while offering the advantage of low melting point, are relatively inferior from the standpoint of vibration resistance and cannot be recommended for use here. For superior mechanical properties, a solder consisting of a few percent silver and the remainder tin and lead, such as 3-5% silver, 35% lead and 6065% tin will serve. An even stronger mechanical bond can be achieved, especially in the case of linings applied by high temperature procedures, by the use of any of a variety of materials known for brazing, such as the standard silver brazing alloys. The procedures followed in obtaining the joint of the present invention by soldering or brazing are those commonplace in the art and require no detailed discussion here.

It is to be understood, of course, that the replacement of the entire front end or tip of the throat plate with ceramic material is by no means essential to the achievement of the objects of the present invention as, indeed, the concept herein disclosed is peculiarly well adapted for the incorporation of a large variety of ceramic fixtures onto a metallic load-bearing base or supporting member so as to take advantage of the exceptional wear-resistant characteristics of ceramic at points of concentrated wear on the base.

Other variations and modifications in the practice of the invention will also be readily apparent to one skilled in the art.

That which is claimed is:

1. In a throat plate for a circular knitting machine in cluding a circular array of knitting needles and at least one yarn guide finger movable into and out of operative position during knitting to feed yarn from the lower end thereof to said needle array, said plate being formed as a flat block-like structure adapted to be mounted on said madhine substantially perpendicular to the axis of said needle array, said structure having a generally radially extending U-shaped channel in the top face thereof and an arcuate end face adjacent to and above said needle array, said U-shaped channel being situated below said guide finger and receiving the lower end thereof when the finger is in operative position, said finger impacting against the channel floor on moving to said operative position and guiding the yarn to be knit through the open end of said channel in said arcuate end face, said yarn running through said open channel end downwardly to said needle array at a substantially constant position during knitting whereby the wear of said running yarn is concentrated in a generaly fixed locus at said end, the improvement wherein a section of said plate adjacent the arcuate end face and containing said locus of concentrated wear is removed and replaced by a pre-formed correspondingly shaped section of wear-resistant ceramic material, said ceramic section comprising the entire tip portion of said throat plate structure bearing said arcuate end face, said ceramic section and said block-like structure having smoothly fitting, mutually adjacent surfaces, the adjacent surface of said ceramic section having adhered thereto a thin metallized coating over substantially its entire area, and a solder joint adhered to said metallized surface and the adjacent surface of said block-like structure to secure 20 said ceramic section to said stnucture, said solder containing at least a minor proportion of silver and said blocklike structure being formed of metal.

2. A throat plate of claim 1 wherein said metallized coating comprises silver.

3. The throat plate of claim 1 wherein said ceramic is an alumina ceramic having an alumina content of at least 85% by weight.

References Cited UNITED STATES PATENTS 2,686,958 8/1924 Eber et a1 29-473.1 2,917,140 12/1959 Omley 29473.1 3,032,294 5/1962 Pieper 242157 3,062,028 11/1962 Mahler et a1. 66--125 3,065,533 11/1962 Dungan et a1 29473.1 X 3,100,339 8/1963 Bondley 29-473.1 3,130,938 4/1964 Dysart 242157 3,132,044 5/ 1964 Pearsall 29-473.1 X 3,182,118 5/1965 De Proost et a1. 29473.1 X 3,284,174 11/1966 Zimmer 29473.l X 3,284,176 11/1966 Reed et a1. 29473.1 X

MERV'IN STEIN, Primary Examiner.

RONALD FELDBAUM, Assistant Examiner. 

